Inspection unit

ABSTRACT

An insulative block has a first face adapted to oppose a board on which an inspection circuit is arranged and a second face adapted to oppose a device to be inspected. The insulative block is formed with first through holes each of which communicates the first face and the second face. A conductive first plating layer is formed on the first face, the second face, and an inner face of at least one of the first through holes. Each of contact probes includes a conductive tubular body held in an associated one of the first through holes and a plunger which is retractably projected from one end of the tubular body and is adapted to come in contact with a terminal of the device.

BACKGROUND

The present invention relates to an inspection unit for ahigh-frequency/high-speed device for ensuring reliable connectionbetween the inspection unit and the device to be inspected, on occasionof inspecting its electrical performance, before a module of ahigh-frequency/high-speed circuit such as an amplifier circuit, a mixercircuit, a filter circuit, a memory, a CPU, etc. or an IC to beincorporated in a mobile phone, for example, is assembled to a circuitboard. In this specification, the term “high-frequency” refers to ananalogue signal having a high-frequency (1 GHz or more), while the term“high-speed” refers to a digital signal having very narrow pulse widthand short pulse interval, and both of which are hereinafter collectivelyreferred to as RF (radio frequency).

On occasion of inspecting electrical performance of the RF device suchas a semiconductor wafer, an IC, or a module, insufficient contactsbetween the terminals may particularly cause fluctuation of impedance orother measurement factors, which may sometimes vary to change measuredvalues. Under the circumstances, such inspection is conducted by aspecial inspection unit, for example, as shown in FIG. 8A (disclosed inJapanese Patent Publication No. 2001-99889A). In such an inspection, anRF circuit, which is the device to be inspected, is constructed in aform of a module 50 including an amplifier circuit and a mixer circuit,and is housed in a metal casing for avoiding interference with theexterior. The module 50 includes input and output terminals 51, 54 forRF signals, a power supply electrode terminal 52, and a groundingterminal 53, which are provided on a back face of the metal casing.Then, the inspection is conducted by electrically connecting theterminals to respective terminals of a wiring board 66 on which certainwirings for the inspection are arranged.

In this example, there are employed contact probes each having a springand a plunger contained in a metal pipe, one end of the plunger beingadapted to be projected to the exterior by the spring and contractedwhen pushed. The respective electrode terminals are connected by contactprobes 63 for RF signals, a contact probe 64 for power supply, and acontact probe 65 for grounding which are contained in a metal block 61for preventing them from being affected by noises. Each of the contactprobes 63 for RF signals is formed in a coaxial structure, using thecontact probe as a core conductor and using an inner wall of a throughhole in the metal block 61 as an outer conductor, especially forpreventing intrusion of noises. In this example, the contact probe is soconstructed that a hollow space is formed between the inner conductor(the RF contact probe 63) and the outer conductor (the inner wall of thethrough hole in the metal block 61) of the coaxial structure so as toobtain a smaller diameter of the contact probe in order to cope with thenarrow pitch. For this reason, insulating O-rings 69 are fitted to thecontact probe 63 for RF signal, as shown in a partially enlarged view ofFIG. 8B, so that the contact probe 63 for RF signal can be held in thehollow space.

Meanwhile, the contact probe 65 for grounding is inserted into the metalblock 61 with a ground socket 65 a being interposed, thereby to avoiddeformation and to obtain favorable contact with the metal block 61. Onthe other hand, the contact probe 64 for power supply is inserted intothe metal block 61 with an insulating tube 64 a being interposed so asnot to come into contact with the metal block 61. In FIG. 8A, denoted bynumeral 67 is a coaxial cable, and 68 is a plate for retaining the metalpipes which form outer shells of the contact probes. Also in the case ofan IC socket for inspecting the IC, the structure around the contactprobe is almost the same, though it has a different outer shape.

As described above, it is possible to reduce a diameter of each throughhole, in a case where a metal block is employed and a coaxial structureis formed by making a hollow space between the inner wall of the metalblock as an outer conductor and a probe for RF signal as an innerconductor. This enables the whole unit can be made small, and it ispossible to inspect even the device in which the electrode terminals areprovided at a narrower pitch, while regulating the impedance. However,it is necessary to form through holes in the metal block 61 formed ofmetal such as brass or aluminum at a pitch of about 0.4 to 1 mm,requiring high manufacturing accuracy of about ±10 μm. Under thecircumstances, there is a problem that it is difficult to substitute themetal block with a die-casting product, and even though it issubstituted with the die-casting product, the through holes must berespectively produced by cutting works, which will lead to enormousincrease of production cost.

Additionally, the probe for power supply must be isolated from the metalblock. In a case where an interval between the contact probes is so setas to have a narrow pitch less than 0.5 mm, for example, a diameter ofthe probe for power supply must be inevitably smaller in order to coverthe contact probe for power supply with an insulating tube. Therefore,there are such problems that cost for inserting the insulating tube willincrease, and that contact resistance will increase in the probe forpower supply.

SUMMARY

It is therefore one advantageous aspect of the invention to easilyprovide, at a low cost, an inspection unit for a high-frequency andhigh-speed device which can regulate high-frequency impedance whilepreventing intrusion of exterior noises as in a unit employing a metalblock, and can use a probe for RF signal having a coaxial structure evenin a case where contact probes (electrode terminals) are arranged at anarrow pitch.

It is also one advantageous aspect of the invention to provide aninspection unit for a high-frequency and high-speed device in which aninner wall of a through hole for a probe which needs not to be shielded,such as a probe for power supply, is not formed as a metal wall, wherebycost for covering a probe for power supply with an insulating tube canbe reduced, and a diameter of the probe for power supply can be made aslarge as possible.

According to one aspect of the invention, there is provided aninspection unit, comprising:

an insulative block, having a first face adapted to oppose a board onwhich an inspection circuit is arranged and a second face adapted tooppose a device to be inspected, the insulative block being formed withfirst through holes each of which communicates the first face and thesecond face;

a conductive first plating layer, formed on the first face, the secondface, and an inner face of at least one of the first through holes; and

a plurality of contact probes, each of which comprises a conductivetubular body held in an associated one of the first through holes and aplunger which is retractably projected from one end of the tubular bodyand is adapted to come in contact with a terminal of the device.

The contact probes may include a signal contact probe adapted totransmit an RF signal and held in one of the first through holes theinner face of which is provided with the first plating layer, in such amanner that a gap is formed between an outer periphery of the tubularbody and the inner face.

The inspection unit may further comprise a retainer, opposing at leastone of the first face and the second face of the insulative block andholding the signal contact probe coaxially with the one of the throughholes. The retainer may comprise: an insulative member, formed with asecond through hole communicating with one of the first through holes;and a conductive second plating layer, formed on at least a part of anouter face of the insulative member and an inner face of the secondthrough hole.

The contact probes may include a power supply contact probe adapted tosupply power. The first through holes may include at least one throughhole an inner face of which is not provided with the first platinglayer, and adapted to hold the power supply contact probe.

With the above configuration, because the plating layer is formed on theinsulative block, it is possible to produce a large number of theinsulative blocks by injection molding or the like, with an accuratesize. Moreover, because the surface of the insulative block is coveredwith the plating layer, the interior of the insulative block can beshielded, and substantially the same function as the metal block can beperformed.

Further, the inner wall of the through hole can serve as the outerconductor of the coaxial structure, while the contact probe for RFsignal is made as the core conductor (the inner conductor) of thecoaxial structure, and the gap between the core conductor and the outerconductor can be made hollow so as to cope with the downsizingrequirement.

Accordingly, the inspection unit according to the invention can bemanufactured very easily, as compared with the case where the throughholes are individually formed in the metal block by drilling work.Therefore, it is possible to perform substantially the same function asthe case where the conventional metal block is employed, while attainingremarkable cost reduction.

Still further, by employing such structure that the plating layer is notprovided in the through hole for inserting the contact probe for powersupply, even when the contact probe for power supply comes into contactwith the inner wall of the through hole in the insulative block, thecontact probe will get in touch with only the exposed face of theinsulative block, because the plating layer is not formed thereon.Accordingly, short circuit will not be formed. Therefore, there is nonecessity of making the contact probe for power supply smaller thanrequired, but the contact probe for power supply can be made as large aspossible in diameter, as far as it can be inserted into the throughhole, and very high performance in terms of contact resistance can bealso obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a section view of an IC socket according to one embodiment ofthe invention.

FIG. 1B is an enlarged section view of contact probes, a grounding blockand a retainer in the IC socket, showing a disassembled state.

FIG. 1C is a section view of one of the contact probes.

FIG. 2 is a perspective, partial section view of through holes formed inthe grounding block.

FIG. 3 is an enlarged section view of contact probes, a grounding blockand retainers in an IC socket according to a modified example.

FIG. 4 is a graph comparing return loss characteristics of contactprobes for RF signal in the IC socket of the invention with those in aconventional IC socket.

FIG. 5 is a graph comparing insertion loss characteristics of thecontact probes for RF signal in the IC socket of the invention withthose in the conventional IC socket.

FIG. 6 is a graph comparing device-side inductance characteristics ofcontact probes for grounding in the IC socket of the invention withthose in the conventional IC socket.

FIG. 7 is a graph comparing board-side inductance characteristics of thecontact probes for grounding in the IC socket of the invention withthose in the conventional IC socket.

FIG. 8A is a schematic section view of a conventional inspection unit.

FIG. 8B is a partial section view of a contact probe in the conventionalinspection unit.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the invention will be described below in detailwith reference to the accompanying drawings.

As shown in FIG. 1B, in an IC socket according to one embodiment of theinvention, an insulative block 21 is provided with through holes 22 intowhich a probe 1SIG for RF signal, a probe 1GND for grounding, and aprobe 1POW for power supply (herein, the probes for low-frequency andlow-speed are treated in the same manner) can be inserted. By providinga plating layer 23 on an outer face of the insulative block 21 and onexposed faces of at least a part of the through holes 22, a groundingblock 2 is formed. The above mentioned probe 1SIG for RF signal, probe1GND for grounding, and probe 1 POW for power supply are inserted intothe through holes 22 in this grounding block 2, and electrode terminalsof a device to be inspected such as an IC (not shown) which is providedon one face of the grounding block 2 are connected to wiring terminalson a wiring board which is provided on the other face of the groundingblock 2 and connected to an inspection device (not shown) by therespective probes 1, whereby inspection is performed.

Specifically, the grounding block 2 is not formed of a metal block, butformed of the plating layer 23 which is provided on the outer face ofthe insulative block 21 such as a resin block and on inner faces of atleast a part of the through holes 22. Grounding the plating layer 23,the grounding block 2 can serve as substantially same as the metal blockprovided in the inspection unit described in the background section ofthe specification.

In this embodiment, one end portion of the contact probe 1 (1SIG, 1GNDand 1POW) is held within the through hole 22 by a recess having astepped part 22 a which is formed on a top face of the insulative block21, while the other end portion of the contact probe 1 is retained by aretainer 3 which is provided on a bottom face of the insulative block21. The plating layer 23 is formed all over the outer faces of theinsulative block 21 and a plating layer 31 a is formed all over theouter faces of an insulative plate 31, the latter being used as theretainer 3.

As shown in FIG. 1A, a device guide 4 is mounted on the upper face ofthe grounding block 2 and positioning pins 6 are inserted into holesformed on the bottom face of the grounding block 2. The IC socket ismounted on a wiring board (not shown) through the use of the positioningpins 6 to connect the respective contact probes 1 to an inspectioncircuit provided on the wiring board. Inserting an inspected device suchas an IC into a recess formed on the device guide 4, terminals of theinspected device are electrically connected to the inspection circuitthrough the contact probes 1.

As shown in FIG. 2, the plating layer 23 is formed by applying platingto the whole outer face of the insulative block 21 and the exposed facesof all the through holes 22 except a through hole 26 for inserting theprobe 1POW for power supply. In this figure, an area where the platinglayer 23 is formed is hatched. The through holes 22 into which the probefor RF signal and a ground socket will be inserted are provided with theplating layer 23 on inner faces thereof as well as on the outer faces.Further, the plating layer 23 is not formed on a circumferential edge ofthe through hole 26.

The plating layer 23 is formed of an Ni plating of about 2 to 3 μm whichis formed by electroless nickel plating for example, and an Au platingof about 3 μm or less which is successively formed thereon byelectroless plating. In this case, a plating resist may be applied to ora plating prevention pin may be inserted into the through hole whichshould not provide with the plating layer, so that the inner face ofsuch a through hole may not get in touch with plating solution, wherebyformation of the plating layer can be easily prevented. Alternatively,it is possible to partly remove the plating layer after the platinglayer is formed on the whole surface.

As described above, the respective probes 1 can be held by theinsulative block 21 provided with the plating layer 23 and theinsulative plate 31 provided with the plating layer 31 b. However, asshown in FIG. 3, it is possible to provide the insulative plates 31 onboth the top and bottom faces of the grounding block 2. In this case,the plating layer 31 b may be formed on the outer faces of therespective insulative plates 31. On the other hand, in a case where theinsulative plates 31 are very thin as compared with the insulative block21, RF performance will not be remarkably deteriorated even though theinsulative plates 31 are not provided with the plating layer 23, so faras the plating layer 23 is formed on the outer face of the insulativeblock 21 and the exposed faces of at least one or some of the throughholes 22.

In the above-mentioned embodiment, the inspection unit can be of thesame structure as the conventional inspection unit employing the metalblock, except that the grounding block 2 is formed by providing theplating layer 23 on the outer face of the insulative block 21.Specifically, as shown in FIGS. 1A and 1B, the contact probes 1 (1SIG,1POW, 1GND) are inserted into the through holes 22 (25, 26, 27 in FIG.2) in the grounding block 2 which is provided with the plating layer 23,and are retained by the retainer 3.

This probe 1SIG for RF signal is formed in a coaxial structure makingthe contact probe 1 inserted into the through hole 25 for the RF signalprobe as an inner conductor and the plating layer 23 formed on theexposed area of the through hole 22 as an outer conductor. The probe1GND for grounding is provided with a ground socket 17 so as to beconnected to the plating layer 23 which is formed in the through hole 27for the grounding probe, and the ground socket 17 is fixed by insertionof the contact probe 1GND for grounding into the ground socket 17. Theprobe 1POW for power supply (including probes for low-frequency andlow-speed signals) is inserted into the through hole 26 for the powersupply probe, where the plating layer is not provided on the inner wallthereof.

However, in a case where there is a sufficient space within the throughhole 26, the plating layer may be also formed on the inner wall thereof,and the probe 1POW for power supply may be inserted into the throughhole 26 while interposing an insulating tube. In the above-mentionedembodiments, the contact probes of a type that a pin at a distal endthereof is movable by a spring or the like are employed. However, anordinary contact pin which is not provided with a movable pin may beemployed.

As shown in FIG. 1C, the contact probe 1 has such a structure that aspring 14 and one ends of the plungers 11, 12 are contained in a metalpipe 13, and the plungers 11, 12 are held so as not to escape from themetal pipe 13 by neck portions 13 a formed in the metal pipe 13, and tobe urged outwardly by the spring 14. When the tip ends of the plungers11, 12 are pressed, the spring 14 will be contracted so that the tipends may be pushed into the metal pipe 13, and while no force isapplied, the tip ends of the plungers 11, 12 are projected by about 1mm, for example. Although the plungers 11, 12 are provided at both endsof the contact probe, depending on the structure of an inspection unit,it may be sufficient that the plunger 11 is provided on at least oneside of the contact probe which comes into contact with the device to beinspected.

The metal pipe 13 has a length of about a few millimeters and may beformed of nickel silver (copper, nickel, zinc alloy) for example. As theplungers 11, 12, a wire member having a diameter of about 0.1 mm andformed of SK material or beryllium copper may be used. The spring 14 maybe formed of a piano wire or the like.

The contact probes 1 may have substantially the same structureirrespective of their uses, namely for signal, for power supply and forgrounding. However, the contact probe 1SIG for RF signal is so formed asto satisfy a prescribed relationship between its outer diameter and aninner diameter of the plating layer 23 inside the through hole 25, inorder to establish the coaxial structure in which the inner wall of thethrough hole 25 in the grounding block 2 as the outer conductor. In acase where the probes are arranged in a matrix manner at a pitch of 0.4mm, the outer diameter of the probes is set to be about 0.15 mm, and theinner diameter of the plating layer 23 is set to be about 0.35 mm. Itwould be desirable that the contact probe 1POW for power supply and thecontact probe 1GND for grounding are as thick as possible, and may beformed having such a size to be inserted into the through holes 26, 27having substantially the same size as the through holes 25 which areformed for the RF signal probes according to the pitch (In a case wherethe ground socket is used, the size will be smaller correspondingly).

The contact probe 1POW for power supply will not cause short circuit,because it is inserted into the through hole 26 which is not providedwith the plating layer 23. However, the contact probe 1POW for powersupply must be covered with the insulating tube which is not shown, in acase where it is inserted into the through hole provided with theplating layer. As to the contact probe 1GND for grounding, the groundsocket 17 formed of phosphor bronze is inserted into the through hole27, as shown in FIG. 1B, for the purpose of improving contact conditionwith the plating layer 23 in the through hole 27, and the contact probe1GND for grounding will be inserted into the ground socket 17.

The insulative block 21 is formed of resin such as polyether imide(PEI), polyimide (PI), polyether ether ketone (PEEK), polyamide imide(PAI), by cutting work, molding work or the like, so that the abovedescribed through holes 22 for the contact probes 1 may be arranged in amatrix manner. Then, the above described plating layer 23 is provided inthe through holes 25, 27 except the through hole 26 for the probe 1POWfor power supply.

Thickness and dimension of this insulative block 21 may vary dependingon its uses, for example, in a case where the inspection unit is used asthe IC socket which simply interconnects the IC and the wiring boardprovided with the wirings, or in a case where the inspection unit isused as an inspecting tool to be connected to a board to which a coaxialcable or the like is connected. But usually, the insulative block 21 isformed having a thickness of about 3 to 8 mm, and an area of 30 to 50 mmsquare.

The retainer 3 includes the insulative plate 31 formed with the platinglayer 31 b on its surface, and an insulating spacer 32 which is providedon an area for the contact probe 1SIG for RF signal. Specifically, thisinsulative plate 31 has a through hole 31 a through which the plunger 11of the contact probe 1 is projected, and in which a stepped part isformed. The insulating spacer 32 is fitted with the stepped part of thethrough hole 31 a, and provided with a through hole 32 a through whichthe plunger 11 of the contact probe 1 is projected, and in which astepped part is formed. More specifically, the stepped part formed inthe insulating spacer 32 is so formed as to fit with an outer shape ofthe metal pipe 13 of the contact probe 1, so that the contact probe 1may not escape from the metal block 2, while the plunger 11 isretractably projected.

The insulative plate 31 is formed of PEI, PI, PEEK or the like in thesame manner as the insulative block 21 in a form of an insulating boardhaving a thickness of about 1 to 2 mm. The insulating spacer 32 isformed of polyether imide (PEI) for example, having a thickness of about0.5 mm. It is to be noted that the through holes 31 a for the probes forgrounding and power supply need not to provide with the insulatingspacer. Denoted by numeral 31 c is a through hole for the positioningpin 8.

In the embodiment shown in FIG. 1B, the retainer is not provided at theupper end side of the contact probe 1, and the stepped part 22 a isformed in the through hole 22. An insulating spacer 32 having the samestructure as described above is fitted with the stepped part, thereby toconstitute the retainer. However, as shown in FIG. 3, it is alsopossible to provide the retainer 3 having the same configuration at theupper end side of the contact probe 1 as well.

In this embodiment, as shown in FIG. 1B, an O-ring 7 formed of siliconerubber or the like is inserted at the lower end side of the probe 1SIGfor RF signal. Each of the contact probes 1 are individually insertedinto the associated through hole 22 from the upper end side thereof.Then, the lower ends of the respective contact probes 1 are collectivelyinserted into the through holes 31 a of the retainer 3. The O-ring 7 isprovided in order to maintain the vertical attitude of the contact probe1 when the lower end side of the contact probe 1 is covered with theretainer 3, thereby avoiding the interference between the lower end ofthe contact probe 1 and the through hole 31 a of the retainer 3.

FIGS. 4 through 7 show comparisons between the conventional inspectionunit employing the metal block and the inspection unit of the inventionin which a grounding block is formed by providing a Ni plating of 2-3 μmin thickness and an Au flash-plating on an insulative block, andretainers provided with no plating are mounted on top and bottom facesof the grounding block, in connection with return loss of the contactprobe for RF signal, insertion loss of the contact probe for RF signal,inductance of the contact probe for grounding at a side of the device,and wiring board-side inductance of the contact probe for grounding. Thecomparisons are made under the same condition. In the figures, Pdesignates the inspection unit of the invention and Q designates theconventional inspection unit. As apparent from the results, it has beenfound that there is no significant difference in high-frequencyperformance between them, and they can be treated in the same manner.

As described above, according to the invention, by forming the platinglayer such as Ni, Au or the like on the surface of the insulative blockformed of resin or the like thereby to constitute the grounding block,it is possible to conduct inspection of the performances which issubstantially equal to the inspection by the structure employing theconventional metal block. It is also possible to produce the groundingblock having the through holes very easily by insertion molding or thelike, without conducting drilling work performed with respect to theconventional metal block. It is also possible to easily obtain thegrounding block by applying the plating layer to the desired places, andhence, remarkable cost reduction can be attained.

Although only some exemplary embodiments of the invention have beendescribed in detail above, those skilled in the art will readilyappreciated that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the invention. Accordingly, all such modifications areintended to be included within the scope of the invention.

The disclosure of Japanese Patent Application No. 2005-374268 filed Dec.27, 2006 including specification, drawings and claims is incorporatedherein by reference in its entirety.

1. An inspection unit, comprising: an insulative block, having a firstface adapted to oppose a board on which an inspection circuit isarranged and a second face adapted to oppose a device to be inspected,the insulative block being formed with first through holes each of whichcommunicates the first face and the second face; a conductive firstplating layer, formed on the first face, the second face, and an innerface of at least one of the first through holes; and a plurality ofcontact probes, each of which comprises a conductive tubular body holdin an associated one of the first through holes and a plunger which isretractably projected from one end of the tubular body and is adapted tocome in contact with a terminal of the device.
 2. The inspection unit asset forth in claim 1, wherein: the contact probes include a signalcontact probe adapted to transmit an RF signal and held in one of thefirst through holes the inner face of which is provided with the firstplating layer, in such a manner that a gap is formed between an outerperiphery of the tubular body and the inner face.
 3. The inspection unitas set forth in claim 2, further comprising: a retainer, opposing atleast one of the first face and the second face of the insulative blockand holding the signal contact probe coaxially with the one of thethrough holes, the retainer comprising: an insulative member, formedwith a second through hole communicating with one of the first throughholes; and a conductive second plating layer, formed on at least a partof an outer face of the insulative member and an inner face of thesecond through hole.
 4. The inspection unit as set forth in claim 1,wherein: the contact probes include a power supply contact probe adaptedto supply power; and the first through holes include at least onethrough hole an inner face of which is not provided with the firstplating layer, and adapted to hold the power supply contact probe.